Ubuntu Builder is a simple tool to build your own distribution. It allows to download, extract, customize in many ways and rebuild your Ubuntu images. You can customize i386 and amd64 images.

Ubuntu Builder Installation:
You can install Ubuntu Builder by downloading the latest version package (here) and installing it using Ubuntu software center by double-clicking on the deb file.

After successful installation, you can open the Ubuntu Builder from Unity 'Dash"

Clicking on 'Select ISO' will open an input box that will allow you to select the ISO image to be extracted for customization.

You can select an ISO image from your local system in or download a Ubuntu Mini Remix which offers ISO image with minimal packages for customization. To do that, click 'Get Ubuntu', choose the release, location, and click Download.